1. Field of the Invention
The present invention relates to the field of soil treatment, and more particularly to a composition and method for soil acidification.
2. Description of Related Art
Acidification of the soil may be needed when soil pH is high, or when carbonates are present, as in semiarid and arid regions. When the pH is above about 7.5, the solubility of phosphorus and the metal micro-nutrients (iron, manganese, and zinc) are severely limited. In more humid regions, farmers may encounter soil alkalinity by over-liming soils, or may be tilling young soils with carbonates from the parent material.
Where carbonates are present in substantial amounts, the cost and amount of material needed to acidify the entire soil may be prohibitive. In such cases, acid forming materials are often banded with fertilizers. This creates a zone of acidification in perhaps 2% of the soil volume, where the solubility of the fertilizers is enhanced at much less cost than by acidifying the entire soil volume.
Of all the acidifying agents, elemental S0 is the most effective per unit weight. For very mole of elemental S0 applied and oxidized, 2 moles of H+ are produced which decreases soil pH.
However, the oxidation rate of finely ground elemental sulfur is slow in cold, alkaline soils. Because of this, spring pre-plant applications of elemental sulfur in the fertilizer band do not effectively change pH by the time seedlings are needing the nutrients in the fertilizer band.
Sulfuric acid works quickly, but is dangerous to work with and requires the use of special acid-resistant equipment. In addition the rapid reaction with soils temporarily creates heat, very acidic conditions, and high salt concentrations, which can kill microorganisms in these zones.
Aluminum sulfate and iron sulfate also work quickly, but are quite expensive. In addition, soluble aluminum from the aluminum sulfate is toxic to plants.
Ammonium polysulfide, (APS), NH4Sx when applied, decomposes into ammonium sulfide colloidal S0. The S0 and S2xe2x88x92 are then oxidized to H2SO4. Potassium polysulfide, (KPS) KS, behaves similarly. The amount of acidity generated is not as much, per unit weight applied, as for elemental sulfur. This material is an expensive source of acidity, unless nitrogen or potassium is also needed.
Ammonium thiosulfate ATS [NH4)2S2O3)] when applied to soil, forms colloidal S0 and ammonium sulfate. The colloidal SO is oxidized to sulfuric acid by microbial processes.
Potassium thiosulfate, or KTS, behaves similarly. These materials do not generate as much acidity per unit weight compared to elemental sulfur, and are too expensive, unless nitrogen or potassium is also needed.
Ammoniated fertilizers will release small amounts of acidity in the soil, but only after the process of nitrification is complete; typically several weeks after soils have warmed in the spring. Where soils are not very alkaline, the effect of several years of nitrification of ammoniated fertilizers is a decline in soil pH.
The acidity from elemental sulfur (S8) results from its oxidation in soil. Although elemental sulfur can be oxidized in the soil by inorganic chemical reactions, this process is usually much slower than microbial oxidation. The rate of biological sulfur (S8) oxidation depends on the interaction of four factors:
1. The presence and diversity of species that oxidize sulfur;
2. The microbial populations of these species in the soil;
3. The physical and chemical characteristics of the S source; and
4. Soil environmental conditions, such as pH, temperature, aeration, and moisture content.
Two general classes of bacteria are involved in S0 oxidation:
Chemoautotrophic S bacterial. This class utilizes energy released from the oxidation of inorganic S for the fixation of CO2 into microbial biomass. The following general equation describes the process.
CO2+S0+1/2O2+2H2Oxe2x80x94CH2O+SO42+2H+
The most important group of S-oxidizing organisms are the chemoautrotrophic bacteria belonging to the genus Thiobacillus. These S0 oxidizers are very active in most soil environments.
The second class of S0 oxidizers occurs in the general population of heterotrophic organisms. Heterotrophic organisms get energy from the oxidation of organic matter. In some soils up to ⅓ of the total heterotrophic population are capable of converting S0 to thiosulfate. The thiosulfate can then be oxidized to sulfate by Thiobacillus.
An increase in temperature increases the S0 oxidation rate in soil, up to an optimum near 30 degrees C. Low springtime soil temperatures are one significant reasons for the slow rate of oxidation and release of acidity. The presence of soil moisture and sufficient aeration is also needed for high rates of sulfur oxidation.
Microorganisms responsible for S0 oxidation require most of the same nutrients needed by plants, plus a few others. Soil organic matter is not essential for the activity of autotrophic S bacteria, but heterotrophic organisms require organic matter as a source of energy.
Carbon dioxide is required by autotrophic microorganisms to oxidize elemental sulfur to sulfuric acid.
CO2+S0+1/2O2+2H2Oxe2x80x94[CH2O]+SO42+2H+
If carbon dioxide levels in soils are low, the rate of sulfur oxidation may be limited. Conditions where CO2 levels are low include low soil temperatures (reduced metabolic activity), low soil organic matter (fewer microorganisms), and crops in early stages of growth.
Considerable variability in S0 oxidation rates among soils exists due to the differences in the number of thiobacillus and S oxidizing heterotrophs. Although the initial rate of S oxidation in laboratory studies can be greatly increased by inoculation with S0 oxidizing organisms, these favorable effects of inoculation are frequently short lived under most conditions, and less benefit is usually obtained in field trials. The simple addition of S0 to soil will encourage the growth of S0 oxidizing microorganisms, modified by environmental factors.
Oxidized lignite is compressed humus, with a density close to lignite, but which has been oxidized by microorganisms and natural processes to the point where the resultant material has a structure and chemical activity that is much like the most humidified portion of soil organic matter.
Humic acids are the major extractable component of oxidized ignites. They have a dark brown to black color. Fulvic acids are present in smaller amounts in these materials, with a light yellow to yellow-brown color. Humin is the fraction of oxidized lignite that is not soluble at any pH, and are black in color. Oxidized lignites contain all three of these fractions, plus varying amounts of mineral matter, depending on its purity. In soils the fulvic acid and varying amounts of the humic acid fraction will dissolve into the soil solution. Heavier humic acids and the humin fraction will remain in the solid phase.
Oxidized ignites can be used to store and buffer both and nutrients and acidity in soils and livestock manure. The chemical basis for this buffer capacity is the cation exchange capacity (CEC) of a material. The cation exchange capacity of raw, ground oxidized ignites is very high varying from about 350 to 800 cmol (+) positive charge per kilogram of material, depending on the relative amounts and proportions of humic +fulvic acids in the material. For comparison, most soils have a CEC of 5-40 cmol (+)/kg. Since the native pH of most oxidized ignites is under 4.5, the majority of the exchange capacity is occupied by acidic cations. Oxidized lignite and its derivatives will complex phosphorus and metal micro nutrients, and increase both the nutrient availability and nutrient uptake of nitrate, phosphorus, and other plant nutrients.
Humic substances also affect a wide range of enzymatic processes, because fulvic acids and lighter fractions of humic acids are actively absorbed and translocated within plants. The effects of these fractions of oxidized lignite on biochemical processes in plants include changes in membrane permeability to nutrient ions, an indoleacetic acid (IAA) hormonal effect by inhibiting IAA-oxidase, and the inhibition and stimulation of several enzymes.
Solution culture, sand culture, soil pot studies and field trials using oxidized lignite and derivatives of humic substances have demonstrated that humic substances will increase root and shoot lengths and mass, number of lateral roots, root initiation, and seedling growth rate and yields. Humic substances may also stimulate the activity of soil microbes. Demonstrated positive effects on Rhizobium, and nitrifying bacteria have been recorded.
As a consequence of the foregoing, there has existed a longstanding need for a new and improved composition and method for soil acidification, and the provision of such is a stated objective of the present invention.
Briefly stated, the present invention provides a composition and method for soil acidification. The composition is provided in a sulfur humate granule. The granule includes elemental sulfur, micronized humate, and a binding agent wherein the ratio of micronized humate to sulfur is about 1:4. The granule is preferably applied to the soil in a band with other fertilizers.